Don't you have a chop with useful queries to use in your daily adventures and desventures with the database?

I include in this first post a list of queries, most of them over Oracle metadata dictionary, and extracted from the site Cibermanuales.com.

I encourage everyone that has his own useful queries or scripts to share it answering to this post. The objective is to create a little online repository that we could consult when we are working with the database.